Searchers have found the body of renowned long-distance runner Micah True, who vanished four days earlier after heading out from a lodge for a morning run in the rugged wilderness near New Mexico's Gila National Forest.

The body was discovered at about 6pm in a remote, rugged area of the Gila Wilderness, the New Mexico state police said. The cause of death was still unknown, but there were no obvious signs of trauma, incident commander Tom Bemis told the Boulder Daily Camera.

True, 58, whose extreme-distance running prowess is detailed in the book Born to Run, set out on what – for him – would have been a routine 12-mile run on Tuesday from The Wilderness Lodge and Hot Springs, where he was staying. He left his dog at the lodge and never returned. A search began the day after.

Though daytime temperatures in south-west New Mexico have been mild of late, temperatures dipped into the mid-20s on recent nights. True left for his run wearing only shorts and a T-shirt and carrying a water bottle.

Michael Sandrock, a columnist who writes about running for the Daily Camera, knew True for at least 20 years and had run with him. He called True a pioneer of the sport of ultrarunning, which involves running extreme distances, often on gruelling terrain and many miles longer than the 26-mile (40km) marathon.

True, he said, had a rebellious spirit but never sought to draw attention to himself even as he became legendary for his talents, which included "just going up and running for hours and hours at a time".

"He's just authentic and genuine … Micah is a guy who follows his bliss," Sandrock said.

He described True as a "legend" among ultra runners.

True was the race director of the Copper Canyon Ultra Marathon, a 50-plus mile race in Urique, Mexico, last month.

He was featured in articles in running magazines and was a central character – known by his nickname, "Caballo Blanco" – in Christopher McDougall's non-fiction bestseller "Born to Run."

McDougall said he based his book on the first Copper Canyon marathon that True organised.

"It's heartbreaking because there was this unique, wonderful running party he put on in the middle of nowhere, and no one else could make this happen," he said.